___________ is known as a coelom derived from blastocoel

The correct answer is Pseudocoel.

To understand why this is the correct answer, let us break down the concepts of embryonic development and body cavities (coelom):

1. Blastocoel formation: During the early stages of embryonic development in animals, a solid ball of cells called the morula hollows out to form a blastula. The fluid-filled cavity inside the blastula is known as the blastocoel.
2. True Coelom vs. Pseudocoel:
- A true coelom is a body cavity that arises within the embryonic mesoderm and is completely lined by mesodermal epithelium (peritoneum).
- A pseudocoel (or pseudocoelom) is a "false" body cavity because it is not completely lined by mesoderm. Instead, it is bounded by ectoderm on the outside and endoderm on the inside.
3. Origin: During development, the blastocoel is not replaced by a true mesoderm-lined coelom. Instead, the blastocoel itself persists into the adult stage as the body cavity. Therefore, a pseudocoel is directly derived from the embryonic blastocoel.

Hence, the body cavity derived from the blastocoel is known as a pseudocoel (found in pseudocoelomate animals like roundworms/Aschelminthes).